NCP1072STAT3G(2012) 查看數據表（PDF） - ON Semiconductor

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NCP1072STAT3G
(Rev.:2012)

High-Voltage Switcher for Low Power Offline SMPS

ON Semiconductor 

NCP1072, NCP1075

Jitter ramp

68.9kHz

65kHz

61.1kHz

adjustable

Internal

sawtooth

Figure 29. Modulation Effects on the Clock Signal by the Jittering Sawtooth

Line Detection

An internal comparator monitors the drain voltage as

recovering from one of the following situations:

• Short Circuit Protection,

• VCC OVP is confirmed,

• UVLO

• TSD

If the drain voltage is lower than the internal threshold

VHV(EN) (91 Vdc typically), the internal power switch is

inhibited. This avoids operating at too low ac input. This is

also called brown−in function in some fields.

Frequency Foldback

The reduction of no−load standby power associated with

the need for improving the efficiency, requires to change the

traditional fixed−frequency type of operation. This device

implements a switching frequency folback when the

feedback current passes above a certain level, IFBfold, set

around 68 mA. At this point, the oscillator enters frequency

foldback and reduces its switching frequency.

The internal peak current set−point is following the

feedback current information until its level reaches Ifreeze.

Below this value, the peak current setpoint is frozen to

88 mA (NCP1072) or 168 mA (NCP1075). The only way to

further reduce the transmitted power is to diminish the

operating frequency down to Fmin (25 kHz typically). This

value is reached at a feedback current level of IFBfold(end)

(100 mA typically). Below this point, if the output power

continues to decrease, the part enters skip cycle for the best

noise−free performance in no−load conditions. Figures 30

and 31 depict the adopted scheme for the part.

Figure 30. By Observing the Current on the Feedback Pin, the Controller Reduces its Switching Frequency for an

Improved Performance at Light Load

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